1. Field of the Invention
The subject of this present invention is a stabiliser for the treatment of the fracture of the neck and upper metaphysis of the femur.
2. Description of the Prior Art
For the treatment of the fracture and fusion complications of the near base of the femur, use is made of angular plates, plate-nail sets and compression hip screws.
The angular plates are built up from an intra-osseous arm in the form of a wedge of various section and an external massive arm. A construction similar to the angular plate is shown by the plate-nail set. In the case of a uniform set the difference involves the external massive arm passing into a middle part in the form of a three-leaf nail. Split plate-nail sets consist of a three-leaf nail screwed to the plate. For the purpose of anastomosing fragments with the angular plate or the plate-nail set, the fragments should be initially locked in place by means of screws or wires. Next, a canal should be chiselled for the intra-osseous part of the plate or nail, drive the intra-osseous arm into the bone and bolt the external arm to the bone shaft.
The disadvantages of the anastomosis by the above-mentioned methods are that the external arm of the angular plate exerts undesired pressure on the bone. The very anastomosis of fractures involves wedging the intra-osseous arm in the fragment being attached, whereby the inter-fragment pressure developed by the implantate is very low.
The known compression hip bolts consist of a massive plate whose one end passes into a bush set at an angle of 135.degree.-150.degree. relative to the plate. A bone bolt is slid into the bush. The bone bolt is locked in place with a small additional metric screw. For the purpose of mounting the screw, it is necessary, among other things, to introduce a directional nail, to drill and tap a hole to screw in the bone bolt, to attach the plate to the bone shaft by means of the bone bolts, and finally, to compress the fragments with the metric screw. The disadvantage of the previously employed method is the disadvantageous pressure of the plate on the bone during the application of the compression hip bolts. Besides, the derotating action of the bolt depends on the magnitude of the compression of the fragments. The amount of the material introduced into the organism is too great and, thus, harmful.
For connecting bone fragments use is also made of bone compression anastomosis sets fulfilling the role of a stabiliser. They consist of a simple plate having round holes with a sliding surface inclined in the direction in which pressure is to be exerted, sets consisting of screws and end-threaded pins, heads and nuts.
The simple plate is fitted on the ends of the screw-pin sets complete with heads and tightened with the nuts. The ability to transmit varying loads by the plate stabiliser is mainly dependent on the reliability of the mechanical joints of the individual components. The previously employed nut has the form of a cylinder with its base shaped as a cone ensuring the strong mounting of the nut in the tapered hole of the plate.
A cross cut has been made in the top surface of the nut for the splines of the nut wrench. The disadvantage of the stabiliser of that type is that it is suitable only for the treatment of long bone fractures due to its construction. The screw-pin set consists of a smooth pin and a screw. The smooth pin does not allow any joint to be obtained with the bone when it is only slid into the hole made in a bone. Consequently, it is not possible to obtain an elastic deformation of the plate, which is required for compressing bone fragments. Thrust discs are individual parts and are applied on screw ends. They rest on the bone and exert pressure thereon, since the pins do not allow the plate to be lifted above the bone.
The force of tightening the nut on the threaded end of the bolt is small due to a low strength of the splines of the wrench. The latter should be accurately aligned with the bolt end since, otherwise, the splines get out of the cuts. Besides, the cuts grow over with tissue and, in order to unscrew the nut, it is necessary to remove the tissue from the cuts.